Hard coatings such as diamond, diamond composite, cubic boron nitride and carbon nitride are in great demand as protective coatings for a number of materials, and as hardness coatings on various machine tools. Diamond coatings are in demand as electronic materials, owing largely to qualities of high thermal conductivity, electron mobility, and radiation resistance. Furthermore, diamond also finds application as a cold cathode material due to its high, negative electron affinity. Such cold cathode applications will make possible flat panel displays. Diamond also has been identified as an excellent drug delivery system candidate due to its chemical inertness, lack of biodegradation, and the ease that various organic molecules have in reversibly binding to its surface.
Because of the great demand, techniques have been developed to apply diamond coatings to a wide variety of materials. Common to most of the production techniques is the formation of a plasma as a source of atomic hydrogen and carbon diamond precursors. Conventional chemical vapor deposition methods require substrate heating to temperatures between 800.degree. to 1000.degree. C., as well as low gas pressures to tens of torr to assure the transformation of carbon precursors from the plasma to a diamond phase on a target substrate. In the flame techniques pioneered by Hirose where diamond growth takes place at atmospheric pressure, target substrates tend to over heat unless actively cooled. In a third case, pressures of tens of thousands of atmospheres and temperatures of thousands of degrees are used to create diamond within molten acetylide salts. Anthony et al., U.S. Pat. Nos. 5,110,579 and 5,273,731, show polycrystaline free standing diamond film and methods of manufacture that include the use of a hot (2000.degree. C.) tungsten filament in a 1 to 50 torr environment of 2% methane and 98% hydrogen to very slowly (16 microns/day) deposit diamond on an 800.degree. C. substrate 7 mm from the filament.
In U.S. Pat. No. 4,981,717 by Stephen Thaler, there is disclosed a method of creating and depositing diamond coatings on a substrate at atmospheric pressure that does not require substrate cooling. The Thaler method is to generate a plasma by absorption of intense impulse of laser radiation into a precursor gas or a gas mixture at atmospheric pressure. The laser impulse is absorbed by an initiator gas, which is mixed in with hydrocarbon precursor gases such as, methane, ethane, propane, ethylene, or acetylene. The initiator is preferably a compound which is strongly absorbing at the output wavelength of the laser. A shock wave, associated with the sudden absorption of laser radiation, is utilized to transport ions, radicals, and molecular fragments onto a suitably positioned substrate so quickly that a diamond like coating is formed. Usually, diamond like coatings are formed of a carbonaceous species having characteristics, hardness and chemical structure similar to diamond.
However there has been a need for a process that rapidly deposits and perhaps welds diamond and other ultrahard on a substrate, or creates diamond or diamond metal composite abrasive particles, or can be used to create diamond patterns on boarings and the like.